Wireless communication system and wireless communication method

ABSTRACT

A format that includes a BSSID of a transmitting station within a preamble of the frame is an HE format, and a format that does not include a BSSID within the preamble but includes a BSSID in a MAC header is a Non-HE format; and a wireless station in the BSS includes a control part which checks a format of a frame received at a predetermined receiver sensitivity or above, and continues demodulation of the received frame if the format is HE format and the BSSID in the received frame is consistent with its own BSS, and stops the demodulation of the received frame if the HE format and the BSSID in the received frame is not consistent with its own BSS.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/764,171, filed Mar. 28, 2018 (now U.S. patent Ser. No. 10/743,346,issued Aug. 11, 2020), which is a U.S. National Stage applicationclaiming the benefit of prior filed International Application NumberPCT/JP2016/079667, filed on Oct. 5, 2016, in which the InternationalApplication claims priority from Japanese Patent Application Number2015-197969, filed on Oct. 5, 2015, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication system and awireless communication method that mitigates a decrease in throughputdue to carrier sense multiple access with collision avoidance (CSMA/CA)protocol carried out by each wireless station, in a wireless local areanetwork (LAN) high density environment.

BACKGROUND ART

In recent years, with the spread of a high-performance portable wirelessstation, such as a notebook computer or a smartphone, wireless LANs incompliance with the IEEE 802.11 standard have come into wide use notonly in companies and public spaces, but also in ordinary houses. As thewireless LANs in compliance with the IEEE 802.11 standard, there are awireless LAN in compliance with the standard IEEE 802.11b/g/n that usesa 2.4 GHz band, and a wireless LAN in compliance with the standard IEEE802.11a/n/ac that uses a 5 GHz band.

At this point, in a wireless LAN high density environment where thenumber of basic service sets (BBSs) is greater than the number ofchannels that are available at the same time in the same place, aplurality of BSSs use the same channel. In that case, due tointerference among the BSSs that use the same channel, throughput of theBSS and throughput of an entire system are decreased. For this reason,in the wireless LAN, autonomous distributed access control calledCSMA/CA that performs transmission of data only when the channel isunoccupied.

However, although the CSMA/CA protocol is performed, in the wireless LANhigh density environment where many wireless LAN networks use the samechannel, because the frequency with which the channel is busy due to thecarrier sense is increased, a transimssion opportunity (an opportunityto obtain the channel access right) is reduced, and throughput isreduced.

When the wireless station performs the carrier sense, a clear channelassessment (CCA) threshold, based on which it is determined whether achannel is idle or busy, using a received signal strength indication(RSSI) of a receive signal, is set. With dynamic sensitivity control(DSC) that dynamically controls the CCA threshold, a technique in whicha state where more defer transmission than is necessary take place isremoved and thus the transmission opportunity is increased has beenstudied (Non-Patent Documents 1, 2, and 3). A control example of the CCAthreshold will be described below, taking, for example, downlinkcommunication from an AP to an STA in which the access point and thestation are defined as the AP and the STA, respectively.

FIG. 14 illustrates a control example of the CCA threshold in therelated art.

In FIG. 14, an AP 1 and an STA 1, an AP 2 and an STA 2, and an AP 3 makeup different BSSs, respectively. The AP 1 possibly selects a default CCAthreshold of −82 dBm and a CCA threshold of −62 dBm for a Non-WLANframe. When a signal that is detected by carrier sense in accordancewith the default CCA threshold is, for example, a signal other than asignal for a wireless LAN, the AP 1 performs control in such a mannerthat changing to a CCA threshold for a Non-WLAN frame takes place andthus a carrier sense range is narrowed down, thereby increasing atransmission opportunity. An example is described here in which the AP 2is located within a carrier sense range in accordance with two CCAthresholds of the AP 1 and in which the AP 3 is located out of a carriersense range in accordance with the default CCA threshold.

The AP 1 starts to perform carrier sense at the default CCA threshold of−82 dBm (S100), and, if a RSSI of a receive signal is at a receiversensitivity of −82 dBm or less (Yes in S101), detects a preamble of thereceive signal (S102). If the preamble is normally detected (Yes inS103), a channel state where setting to the default CCA threshold atwhich the detection of the preamble is successful takes place isdetermined as is (S104). At this point, if a channel is busy (Yes inS105), demodulation of the receive signal is continued (S106), and ifthe channel is idle (No in S105), the demodulation of the receive signalis stopped (S107). On the other hand, if the preamble is not normallydetected (No in S103), changing to the CCA threshold of −62 dBm for theNon-WLAN frame takes place and a transmission opportunity is caused tobe increased by narrowing down the carrier sense range and determiningthe channel state (S108).

In the CCA threshold control described above, in the AP 1, even if thepreamble can be normally detected when a signal of the AP 3 is atreceiver sensitivity or above, the channel is determined to be idle bysetting the CCA threshold to the default value, and the demodulation isstopped. Thus, the transmission opportunity can be caused to beincreased. That is, the AP 1 and the AP 3 possibly perform simultaneoustransmissions with mutual interference being decreased. On the otherhand, regarding a signal of the AP 2, the channel is busy by causing thesetting to the default CCA threshold to take place. The AP 1 continuesthe demodulation of the signal of the AP 2 and defers transmission. Atthis point, although the simultaneous transmissions from the AP 1 to theSTA 1 and from the AP 2 to the STA 2 are possible, the detection of thesignal of the AP 2 causes the AP 1 to defer transmission and to be in astate of a so-called exposed station. For example, regarding the AP 1,if it can be detected that a signal of another BSS is present and if theCCA threshold is controlled in a manner that causes the CCA threshold tobe high and the corresponding carrier sense range is narrowed down,although the AP 2 is performing the transmission, the simultaneoustransmission by the AP 1 is possible and system throughput is improved.

However, if the STA 1 is located near the AP 2 and an interferencesignal from the AP 2 is large in magnitude, although the control of theCCA threshold in the AP 1 causes the transmission opportunity of the AP1to be increased, there is a concern that a receive failure will occur inthe STA 1 due to the interference signal from the AP 2, thereby insteaddecreasing throughput.

Furthermore, in the AP 1, if a signal that is transmitted by the STA 1under control is received, or if a beacon frame that is transmitted bythe AP 2 is received, it can be said that the AP 1 may be kept fromperforming the transmission and perform the reception, rather thancontrolling the CCA threshold and increasing the transmissionopportunity. That is, it is desirable that the AP 1 distinguishesbetween the signal from the STA 1 in the BSS that the AP 1 itself makesup, and the signal from the AP 2 in another BSS, and that AP 1 canselect whether or not the CCA threshold is controlled and thus thesimultaneous transmissions are set to be possible, depending on whetheror not the demodulation of the signal from the AP 2 in the another BSSis also necessary.

-   Non-Patent Document 1: “Proposed Specification Framework for TGax”,    Robert Stacey et al., doc.:IEEE 802.11-14/1453r2, 5 Nov. 2014-   Non-Patent Document 2: The LAN/MAN Standards Committee”, IEEE Std    802.11TM 2012 IEEE standard for Information    Technology—Telecommunications and information exchange between    systems—Local and metropolitan area networks Specific requirements    Part 11:Wireless LAN Medium Access Control (MAC) and Physical PHY.-   Non-Patent Document 3: Graham Smith, “Dynamic Sensitivity Control    Practical Usage”, doc.: IEEE 802.11-14/0779r2

Disclosure Problems to be Solved

Incidentally, a technology has been considered in which a highefficiency (HE) format that includes a field of a BSS identifier (BSSID)within a PHY preamble of a wireless LAN frame is used to determinewhether a signal is a signal of a BSS that the wireless station itselfmakes up and a signal of another BSS, and in which simultaneoustransmissions are performed in such a manner that throughput can bemaximized.

Wireless stations, an AP and an STA, which possibly transmit and receivea frame in an HE format, are defined as HE stations. On the other hand,a format in the related art, which does not include a field for a BSSIDand includes a preamble, such as L-SIG, L-STF, and L-LTF is a Non-HEformat, and wireless stations, an AP and an STA that do not particularlyhave a function of transmitting and receiving a frame in the HE format,but possibly transmit and receive a frame in Non-HE format are definedas Non-HE stations.

FIG. 15 illustrates an example of a configuration of wirelesscommunication system in which a wide variety of stations are present.

In FIG. 15, a transmitting station 11 is the HE station, and destinationstations 12 and 13 that are in the same BSS as the transmitting station11, are set to be the HE station and the Non-HE station, respectively.That is, the transmitting station 11 transmits a frame in the HE formator a frame in the Non-HE format in compliance with standards for thedestination station. An interfering station 14 that is an interferingsource for the transmitting station 11 and the destination station 12 isthe HE station, and an interfering station 15 that is an interferingsource for the transmitting station 11 and the destination station 13 isthe Non-HE station.

At this point, the transmitting station 11 distinguishes between a framein the HE format that is transmitted from the interfering station 14,and a frame in the Non-HE format that is transmitted from theinterfering station 15. Moreover, if the frame in the HE format ispresent, the BSSID is detected. Then, depending on whether the detectedBSSID is consistent with a BBS that the transmitting station 11 makesup, it is determined whether or not the simultaneous transmissions arepossible, or it is determined whether or not the simultaneoustransmissions are kept from being performed and the frame has to bereceived.

For example, the transmitting station 11 recognizes the frame in the HEformat that is transmitted from the interfering station 14. If it isdetermined that a signal of another BSS is present, the transmittingstation 11 stops the demodulation and possibly performs transmission tothe destination stations 12 and 13. At this time, in the same manner, ifthe demodulation is stopped, the destination station 12 that canrecognize the frame in the HE format possibly perform the reception fromthe transmitting station 11 as well, but because the destination station13 cannot recognize the frame in the HE format, the destination station13 continues the reception without any processing. In this case, thetransmitting station 11 recognizes the frame in the HE format from theinterfering station 14, stops the demodulation, and transmits the framein the Non-HE format to the destination station 13. Although this is thecase, there is a likelihood that the reception will fail in thedestination station 13 which is continuing the reception of the framefrom the interfering station 14. That is, the transmitting station 11effectively performs control in which in compliance with a signal fromthe interfering station 14 and standards for the destination stations 12and 13, it is determined whether or not the simultaneous transmissionsare performed, and in which the simultaneous transmissions are allowedfor the destination station 12 that is the HE station and thesimultaneous transmissions are disallowed for the destination station 13that is the Non-HE station.

A proposition of the present invention is to provide a wirelesscommunication system and a wireless communication method that arecapable of efficiently acquiring a transmission opportunity with controlof a CCA threshold in a wireless LAN high density environment in whichan HE station and a Non-HE station are mixedly present, and are capableof not only improving system throughput and but also efficientlyacquiring a management frame necessary for information collection, suchas a beacon frame.

Means for Solving the Problems

According to a first invention, there is provided a wirelesscommunication system in which a plurality of adjacent BSSs, made of aplurality of wireless stations, which transmit and receive a frame usinga predetermined channel, are present and in which a transmitting stationof each BSS performs wireless communication by access control based onCSMA/CA using aCCA threshold considering an interference power from aninterfering station which uses the predetermined channel, in which aformat that includes a BSSID of a transmitting station within a preambleof the frame is an HE format, and a format that does not include a BSSIDwithin the preamble but includes a BSSID in a MAC header is a Non-HEformat; and the wireless station in the BSS includes a control partwhich checks a format of a received frame received at a predeterminedreceiver sensitivity or above, and continues demodulation of thereceived frame if the format is HE format and the BSSID in the receivedframe is consistent with its own BSS, and stops the demodulation of thereceived frame if the format is the HE format and the BSSID in thereceived frame is not consistent with its own BSS.

In the wireless communication system according to the first invention,the control part is configured to change the CCA threshold from adefault value to a CCA threshold for the HE format and perform carriersense when the received frame is in the HE format and the BSSID of thereceived frame is not consistent with its own BSS.

In the wireless communication system according to the first invention,the control part is configured, when a format of the received frame isthe Non-HE format, to change the CCA threshold from a default value to aCCA threshold for the Non-HE format and perform carrier sense, and tocontinue the demodulation of the received frame if the predeterminedchannel is busy, and to stop the demodulation of the received frame ifthe predetermined channel is idle.

In the wireless communication system according to the first invention,the control part is configured, when a format of the received frame isthe Non-HE format, to check the BSSID included in the received frame, tocontinue the demodulation of the received frame if the BSSID isconsistent with its won BSS, and to stop the demodulation of thereceived frame if the BSSID is not consistent with its own BSS.Moreover, in the wireless communication system according to the firstinvention, the control part is configured to change the CCA thresholdfrom a default value to a CCA threshold for the Non-HE format andperform carrier sense when the received frame is in the Non-HE formatand the BSSID is not consistent with its own BSS.

In the wireless communication system according to the first invention,the control part is configured when a format of the received frame isthe Non-HE format, to check a type of the received frame and to continuethe demodulation if the type is a frame type or a frame subtypenecessary for communication control of each the wireless station.

In the wireless communication system according to the first invention,the control part is configured to check a destination station to which aframe is scheduled to be transmitted, to control the CCA threshold to avalue higher than a default value if the destination station and its ownstation can stop the demodulation of the received frame, and to notcontrol the CCA threshold or the CCA threshold so that the frame can bereceivable if the destination station and its own station cannot stopthe demodulation of the received frame.

In the wireless communication system according to the first invention,the control part is configured to check a format of a frame scheduled tobe transmitted, and to control the CCA threshold to a value higher thanthe default value if the format is the HE format, and to not control theCCA threshold or control the CCA threshold so that the frame can bereceivable if the format is the Non-HE format.

In the wireless communication system according to the first invention,the control part is configured to check a type of a frame scheduled tobe transmitted, and to not control the CCA threshold or control the CCAthreshold so that the frame can be receivable if the type is a frametype or a frame subtype necessary for communication control of eachwireless station, and to control the CCA threshold to a value higherthan the default value if the type is not the frame type or the framesubtype necessary for the communication control of each wirelessstation.

According to a second invention, there is provided a wirelesscommunication method in which a plurality of adjacent BSSs, made of aplurality of wireless stations, which transmit and receive a frame usinga predetermined channel, are present and in which a transmitting stationof each BSS performs wireless communication by access control based onCSMA/CA using a CCA threshold considering an interference power from aninterfering station which uses the predetermined channel, in which aformat that includes a BSSID of a transmitting station within a preambleof the frame is an HE format, and a format that does not include theBSSID within the preamble but includes a BSSID in a MAC header is aNon-HE format; and the wireless station in the BSS has a first stepchecking a format of a frame received at a predetermined receiversensitivity or above; and a second step continuing demodulation of thereceived frame if the format is HE format and the BSSID in the receivedframe is consistent with its own BSS, and stopping the demodulation ofthe received frame if the format is the HE format and the BSSID in thereceived frame is not consistent with its own BSS.

In the wireless communication method according to the second invention,the second step further changes the CCA threshold from a default valueto a CCA threshold for the HE format and performs carrier sense when thereceived frame is in the HE format and the BSSID of the received frameis not consistent with its own BSS.

In the wireless communication method according to the second invention,the second step further changes the CCA threshold from a default valueto a CCA threshold for the Non-HE format and performs carrier sense whena format of the received frame is the Non-HE format; and continues thedemodulation of the received frame if the predetermined channel is busy;and stops the demodulation of the received frame if the predeterminedchannel is idle.

In the wireless communication method according to the second invention,the second step further checks the BSSID included in the received framewhen a format of the received frame is the Non-HE format; and continuesthe demodulation of the received frame if the BSSID is consistent withits own BSS; and stops the demodulation of the received frame if theBSSID is not consistent with its own BSS. In the wireless communicationmethod according to the second invention, the second step changes theCCA threshold from a default value to a CCA threshold for the Non-HEformat and performs carrier sense when the received frame is in theNon-HE format and the BSSID is not consistent with its own BSS.

In the wireless communication method according to the second invention,the second step checks a type of the received frame when a format of thereceived frame is the Non-HE format, and continues the demodulation ifthe type is a frame type or a frame subtype necessary for communicationcontrol of each the wireless station.

The wireless communication method according to the second inventionfurther includes a third step checking a destination station to which aframe is scheduled to be transmitted, controlling the CCA threshold to avalue higher than the default value if the destination station and itsown station can stop the demodulation of the received frame, and notcontrolling the CCA threshold or controlling the CCA threshold so thatthe frame can be receivable if the destination station and its ownstation cannot stop the demodulation of the received frame.

The wireless communication method according to the second inventionfurther includes a fourth step checking a format of a frame scheduled tobe transmitted, controlling the CCA threshold to a value higher than thedefault value if the format is the HE format, and not controlling theCCA threshold or controlling the CCA threshold so that the frame can bereceivable if the format is the Non-HE format.

The wireless communication method according to the second inventionfurther includes a fifth step checking a type of a frame scheduled to betransmitted, not controlling the CCA threshold or controlling the CCAthreshold so that the frame can be receivable if the type is a frametype or a frame subtype necessary for communication control of eachwireless station, and controlling the CCA threshold to a value higherthan the default value if the type is not the frame type nor the framesubtype necessary for the communication control of each wirelessstation.

Effects

According to the present invention, dynamic control of a CCA thresholdaccording to an interference power not only increases a transmissionopportunity, but also stops demodulation processing of an interferenceframe and makes transmission processing and receiving processingpossible. Thus, an improvement in throughput is achieved whiletransmissions are positively performed despite the interference frame.

Furthermore, a type of a receive frame is determined while simultaneoustransmissions are positively utilized with the control of the CCAthreshold or with the control of continuing/stopping of the demodulationprocessing. If data frame is not present, demodulation processing iscontinued and thus a management frame, such as a beacon frame, can bereliably received.

Furthermore, when it comes to a Non-HE station that cannot controlstopping of the demodulation processing of the interference frame, whilesimultaneous transmissions are positively utilized with the control ofthe CCA threshold or with the control of the continuing/stopping of thedemodulation processing, according to the standard and supportedfunctionalities of a destination station for a transmit frame, the CCAthreshold is not controlled, or control is performed in a manner thatcauses the CCA threshold to be a CCA threshold at which the interferenceframe is detectable. Thus, the simultaneous transmissions to the Non-HEstation are avoided and a decrease in throughput can be avoided.

Furthermore, if the transmit frame is not in an HE format, whilesimultaneous transmissions are positively utilized with the control ofthe CCA threshold or with the control of the continuing/stopping of thedemodulation processing, the CCA threshold is not controlled, or controlis performed in a manner that causes the CCA threshold to be a CCAthreshold at which the interference frame is detectable. Thus, thesimultaneous transmissions to the Non-HE station are avoided and thedecrease in throughput can be avoided.

Furthermore, if the transmit frame is the management frame, whilesimultaneous transmissions are positively utilized with the control ofthe CCA threshold or with the control of the continuing/stopping of thedemodulation processing, the CCA threshold is not controlled, or controlis performed in a manner that causes the CCA threshold to be a CCAthreshold at which the interference frame is detectable. Thus, thesimultaneous transmissions are avoided and the decrease in throughputcan be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of awireless communication system according to the present invention.

FIG. 2 is a flowchart illustrating a first example of a procedure for anAP 1 to perform receiving processing in a second embodiment of thepresent invention.

FIG. 3 is a timing chart illustrating an example of operations in StepsS8 and S12.

FIG. 4 is a timing chart illustrating a first example of operations inSteps S14 and S15.

FIG. 5 is a timing chart illustrating a second example of the operationsin Steps S14 and S15.

FIG. 6 is a flowchart illustrating a second example of the procedure forthe AP 1 to perform the receiving processing in a second embodiment ofthe present invention.

FIG. 7 is a timing chart illustrating an example of operations in StepsS21, S23, and S24.

FIG. 8 is a flowchart illustrating an example of the procedure for theAP 1 to perform the receiving processing in a third embodiment of thepresent invention.

FIG. 9 is a timing chart illustrating an example of operations in StepsS10 to S13, S31, and S32.

FIG. 10 is a flowchart illustrating an example of the procedure for theAP 1 to perform transmitting processing in a fourth embodiment of thepresent invention.

FIG. 11 is a timing chart illustrating an example of operations in StepsS44 and S45.

FIG. 12 is a flowchart illustrating a first example of a procedure forthe AP 1 to perform the transmitting processing in a fifth embodiment ofthe present invention.

FIG. 13 is a flowchart illustrating a second example of the procedurefor the AP 1 to perform the transmitting processing in the fifthembodiment of the present invention.

FIG. 14 is a diagram illustrating an example of control of a CCAthreshold in the related art.

FIG. 15 is a diagram illustrating an example of a configuration of awireless communication system in which a wide variety of stations arepresent.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an example of a configuration of a wirelesscommunication system according to the present invention.

In FIG. 1, an AP 1, an AP 2, an AP 3, and an AP 4 make up differentBSSs, respectively, and the AP 1 and an STA 1-1, an STA 1-2, and an STA1-3 make up the same BSS. It is possible that as a CCA threshold of theAP 1, −82 dBm is selected as default and that −76 dBm is selected for aNon-HE format, −66 dBm for an HE format, and −62 dBm for a Non-WLANframe. A carrier sense range of the AP 1 is one that depends on the CCAthreshold, and is indicated here by a circle for simplicity. Receiversensitivity is assumed here to be a predetermined value of −82 dBm orless. It is noted that numerical values of the CCA threshold and thereceiver sensitivity, as well as default values thereof, are examples.

With respect to the AP 1, the STA 1-1 and the STA 1-3 are present withina carrier sense range in accordance with a CCA threshold of −62 dBm forthe Non-WLAN frame. With respect to the AP 1, the AP 3 is presentbetween the carrier sense range in accordance with the CCA threshold of−62 dBm for the Non-WAN frame and a carrier sense range in accordancewith a CCA threshold of −66 dBm for the HE format. With respect to theAP 1, the AP 2 and the STA 1-2 are present between the carrier senserange in accordance with the CCA threshold of −66 dBm for the HE formatand a carrier sense range in accordance with a CCA threshold of −76 dBmfor the Non-HE format. With respect to the AP 1, the AP 4 is presentbetween the carrier sense range in accordance with the CCA threshold of−76 dBm for the Non-HE format and a carrier sense range accordance witha default CCA threshold of −82 dBm. In the AP 1, interference from theAP 2 to the AP 4 is observed according to the CCA threshold that is setin advance.

At this point, the AP 1, the STA 1-1, the STA 1-2 are assumed to be HEstations, and the STA 1-3 is assumed to be a Non-HE station. Therefore,the AP 1 transmits a frame at the HE format, which is destined for theSTA 1-1 and the STA 1-2, and the AP1 transmits a frame at the Non-HEformat, which is destined for the STA 1-3. A frame which is destined forthe STA 1-1 and the STA 1-3 is assumed to be present in a transmissionqueue in the AP 1.

A control example in which a transmission opportunity is efficientlyacquired in the AP 1 and system throughput is improved, and a controlexample in which a frame necessary for information collection, such as abeacon frame, is also efficiently acquired will be described below. In afirst embodiment, a control example of a communication area resultingfrom setting the receiver sensitivity is described. In a secondembodiment, a control example of each receive frame format is described.In a third embodiment, a control example of each receive frame type isdescribed. In a fourth embodiment, an example of control for eachstandard of a destination station and each of the supportedfunctionalities of the destination station is described. In a fifthembodiment, a control example of each transmit frame format or type isdescribed.

First Embodiment

In the first embodiment, it is assumed that all stations which have toperform communication with the AP 1 are placed within a range of asingle-digit meter in which tethering is performed. For example, in FIG.1, if only the STA 1-1 and the STA 1-3 are present in the vicinity ofthe AP 1, receiver sensitivity of the AP 1, for example, is set to −62dBm or more. Accordingly, it is possible that the AP 1 performssimultaneous transmissions to the STA 1-1 and the STA 1-3 more simplythan the AP 1 controls the CCA threshold.

A control server, which is connected to each AP in a shared manner andin a wired or wireless manner, can set receiver sensitivity thatcorresponds to a communication area, which is controlled by each AP. InFIG. 1, the AP 1 measures receive signals from the STA 1-1 and the STA1-3 or RSSIs of wireless signals that are transmitted from the AP 2 toAP 4 in the vicinity, and notifies the control server of results of themeasurement. If the RSSIs from the STA 1-1 and the STA 1-3, which aremeasured by the AP 1, are sufficiently strong, the control serverdetermines that the station is present close to the AP 1, and controlsthe receiver sensitivity. The receiver sensitivity, for example, is avalue that is equal to or lower than the RSSIs from the STA 1-1 and theSTA 1-3, and is set to be stronger than RSSIs from the AP 2 to the AP 4in the vicinity, which are measured by the AP 1.

Furthermore, if a transmitted signal strength indication or an antennagain of each STA or each AP is known, a RSSI from each STA or each APmay be corrected using these values. However, if it is determined that aRSSI from the AP 1, which is measured in the AP 2 to AP 4, causes aninterference in any of the AP 2 to AP 4, and that throughput decreases,the receiver sensitivity of the AP 1 may not be controlled.

Second Embodiment

A feature of the second embodiment is that a CCA threshold of eachreceive frame format in the AP 1 is controlled. At this point, the CCAthreshold is controlled to be a high value, for example, −66 dBm that isillustrated in FIG. 1, in such a manner that the simultaneoustransmissions are positively performed in a frame in the HE format. Fromthe perspective of the fairness, when it comes to a frame in the Non-HEformat, the CCA threshold is controlled to be a default value, forexample, −82 dBm that is illustrated in FIG. 1, or to be a value that islower than the CCA threshold for the HE format, for example, −76 dBmthat is illustrated in FIG. 1. It is noted that the CCA threshold forthe HE format may be set to be in a fixed relationship to the CCAthreshold for the Non-HE format, for example, be set to be higher by 10dB, and so forth.

FIG. 2 illustrates a first example of a procedure for the AP 1 toperform receiving processing in the second embodiment of the presentinvention. It is noted that this holds true for another AP and STA.

In FIG. 2, the AP 1 starts to perform carrier sense at the default CCAthreshold of −82 dBm (S0), and, if a received signal strength indication(RSSI) of a receive frame is at a receiver sensitivity of −82 dBm orbelow (Yes in S1), detects a preamble of the receive frame (S2). If thepreamble is normally detected (Yes in S3), it is checked whether frameformat is the HE format or the Non-HE format (S4). If the frame formatis the HE format (Yes in S5), a BSSID in the preamble is checked (S6).If a BSSID of the receive frame is the BSSID of the AP 1 (Yes in S7),demodulation of the receive frame is continued (S8).

Furthermore, if the preamble of the receive frame is not detectednormally in Step S3 (No in S3), it is determined that a wireless LANframe is not present, setting to a CCA threshold of −62 dBm for theNon-WLAN frame takes place, and a channel state is determined (S9). Thiscontrol is the same as that in Step S108, which is illustrated in FIG.14. Narrowing down to the carrier sense range and determination of thechannel state can cause the transmission opportunity to be increased.

Furthermore, if in Step S5, the receive frame is not in the HE format(No in S5), setting to the CCA threshold of −76 dBm for the Non-HEformat takes place and the channel state is determined (S10). At thispoint, if a channel is busy (Yes in S11), the demodulation of thereceive frame is continued (S12) and the simultaneous transmissions aredeferred. On the other hand, if the channel is idle (No in S11), thedemodulation of the receive frame is stopped (S13), and a state wherethe simultaneous transmissions are possible is set to be entered.

Furthermore, in Step S7, if the BSSID of the receive frame is notconsistent with the BSSID of the AP 1 (No in S7), because a frame in theHE format from another BSS is received, setting to a CCA threshold of−66 dBm for the HE frame takes place and the channel state is determined(S14). Then, despite the fact that the channel is busy or idle, thedemodulation of the receive frame is stopped (S15), and the simultaneoustransmissions are set to be performed.

FIG. 3 illustrates an operational example of Steps S6 to S8 and S10 toS12. An example of an operation by the AP 1 that is to be performed whenthe frame in the HE format that is transmitted by the STA 1-2 isreceived and the frame in the Non-HE format that is transmitted by theAP 2 is received is described here.

In FIG. 3, at time t1, the AP 1 detects a RSSI that is stronger than thereceiver sensitivity and starts to receive a frame. At time t2, the AP 1normally receives the preamble of the receive frame, checks that the HEformat is present, checks that the BSSID is the same as that of the BSSthat the AP 1 itself makes up, and then continues the demodulation. Attime t3, the AP 1 completes the frame demodulation. In this case,because it is determined that the received frame is a frame of the STA1-2 that the AP 1 itself makes up, which needs to be demodulated, thedemodulation is continued and the simultaneous transmissions are notperformed.

It is noted that, if the frames in the HE format that are transmitted bythe AP 2 to AP 4 are received, because the simultaneous transmissionsare performed after the preamble is received in the processing in StepS15, the demodulation is stopped, but a description will be made of thatwith reference to FIGS. 4 and 5.

At time t4, the AP 1 detects the RSSI that is stronger than the receiversensitivity and starts to receive the frame. At time t5, the AP 1normally receives the preamble of the receive frame, checks that theNon-HE format is present, and causes the setting to the CCA threshold of−76 dBm for the Non-HE format to take place in the processing in StepS10. In the present example of the operation, because the frame is thereceive frame from the AP 2 and the RSSI exceeds the CCA threshold, itis determined that the channel is busy and the demodulation is continuedand the frame demodulation is completed at time t6. In this case,because a frame in the Non-HE format that is transmitted by the AP 2that makes up another BSS is present, it is determined that there is alikelihood that the demodulation will be needed as is the case with, forexample, the beacon frame or the like, and thus the demodulation iscontinued and the simultaneous transmissions are not performed. In thismanner, although the CCA threshold is high, if the channel is busy, thesimultaneous transmissions are avoided, and thus an influence of aninterference on another BSS that is receiving the frame can be reduced.

On the other hand, when the setting to the CCA threshold of −76 dBm forthe Non-HE format takes place in the processing in Step S10, because theRSSI from the AP 4 falls below the CCA threshold, the AP 1 that receivesthe frame in the Non-HE format from the AP 4 determines that the channelis idle, and the demodulation is stopped in the processing in Step S13.Thus, the simultaneous transmissions are possible. It is noted that thereception of the frame in the Non-HE format, such as the beacon framethat is transmitted by the AP 4 is possibly dealt with according to aprocedure that will be described below in the third embodiment.

FIG. 4 illustrates a first example of operations in Steps S14 and S15.An example of an operation by the AP 1 that is to be performed when theframe in the HE format that is transmitted by the AP 2 is received isdescribed here.

In FIG. 4, the STA 1-1 and the AP 1 detect the RSSI that is strongerthan the receiver sensitivity and start to receive the frame, at timest7 and t8, and normally receive the preamble of the receive frame andcheck that the HE format is present, at times t9 and t10. At this point,because the BSSID indicates that the AP 2 makes up another BSS, thesetting to the CCA threshold of −66 dBm for the HE format takes place inthe processing in Step S14 and the demodulation is stopped in theprocessing Step S15. In the present example of the operation, when theAP 1 performs the recognition as the frame from the AP 2 and raises theCCA threshold, because the RSSI falls below the CCA threshold of the AP1, it is determined that the channel is idle, and the demodulation isstopped. Thus, the simultaneous transmissions are possible.

If the channel is idle until time t11 at which a fixed time+a randomtime have elapsed, the AP 1 transmits a frame that is destined for theSTA 1-1. The STA 1-1 stops the demodulation at time t9, and detects theRSSI that is stronger than the receiver sensitivity and starts toreceive the frame, at time t12.

In this manner, after detecting the preamble of the frame in the HEformat that is transmitted by the AP 2 that makes up another BSS, the AP1 causes setting to a high CCA threshold for the HE format to take placeand stops the demodulation. Because of this, the AP 1, along with the AP2, easily acquires the transmission right and performs the simultaneoustransmissions. On the other hand, the STA 1-1 also stops thedemodulation after detecting the preamble of another BSS, and, althoughthe AP 2 is transmitting the frame, can normally demodulate the framethat is transmitted by the AP 1.

FIG. 5 illustrates a second example of the operations in Steps S14 andS15. An example of an operation by the AP 1 that is to be performed whenthe frame in the HE format that is transmitted by the STA 1-2 isreceived after the frame in the HE format that is transmitted by the AP3 is received is described here.

In FIG. 5, the AP 1 detects the RSSI that is stronger than the receiversensitivity and starts to receive the frame, at time t13, and normallyreceives the preamble of the receive frame and checks that the HE formatis present, at time t14. At this point, because the BSSID indicates theAP 3 that makes up another BSS, the setting to the CCA threshold of −66dBm for the HE format takes place in the processing in Step S14 and thedemodulation is stopped in the processing in Step S15. In the presentexample of the operation, although the AP 1 performs the recognition asthe frame from the AP 3 and raises the CCA threshold, because the RSSIexceeds the CCA threshold of the AP 1, it is determined that the channelis busy, and the simultaneous transmissions are deferred.

On the other hand, the STA 1-1 and the STA 1-2 also receive the frame inthe HE format from the AP 3 and stops the demodulation. If the channelis idle, the STA 1-1 and the STA 1-2 possibly perform the transmission.At this point, if the RSSI from the AP 3 falls below the CCA thresholdof −66 dBm for the HE format in the STA 1-2, it is determined that thechannel is idle, and a frame that is destined for the AP 1 istransmitted. The AP 1 stops the demodulation of the frame from the AP 3,at time t14, and detects the RSSI that is stronger than the receiversensitivity and starts to receive the frame from the STA 1-2, at timet15.

In this manner, after detecting the preamble of the frame in the HEformat that is transmitted by the AP 3 that makes up another BSS, the AP1 causes the setting to the high CCA threshold for the HE format to takeplace and stops the demodulation, but the RSSI of the frame from the AP3 is stronger than the CCA threshold of the AP 1, the channel is busyand the simultaneous transmissions are deferred without being performed.On the other hand, after detecting the preamble of another BSS, the STA1-2 raises the CCA threshold and stops the demodulation, and if thechannel is idle, the transmission of the frame is possible. However,although the AP 3 is transmitting a frame, if the STA 1-2 can transmit aframe, the AP 1 can normally demodulate the frame.

In examples in FIG. 4 and FIG. 5, if, with the BSSID that is detected asa result of demodulating the preamble of the frame in the HE format inthe processing in each of Steps S6 and S7 in FIG. 2, it is determined inthe AP 1 that the frame from the AP 2 or the AP 3 that makes up anotherBSS is present, the default CCA threshold of −82 dBm is raised to theCCA threshold of −66 dBm for the HE format in the processing in Step S14in FIG. 2. At this point, the frame of the AP 2 is not detected and thechannel is idle. The frame of the AP 3 remains detected and the channelis busy. However, any AP 1 stops the demodulation. In the example inFIG. 4, the AP 1 possibly performs the transmission and in the examplein FIG. 5, the AP 1 possibly performs the reception.

Incidentally, if the receive frame is in the HE format and is determinedas the frame of another BSS in the processing in each of Steps S6 and S7in FIG. 2, in some cases, it is also desirable that in the AP 1, when itcomes to a form of the receive frame, the channel is set to be busywithout performing processing that controls the CCA threshold that isdescribed with reference to Step S14.

For example, in new wireless LAN specifications, a functionality isassumed that allows a plurality of STAs which receive a trigger framefrom the AP to simultaneously transmit a UL MU frame to the AP usinguplink (UP) multi-user MIMO (MU-MIMO). If another AP starts to performtransmission to the trigger frame, the STA cannot transmit the UL MUframe, or although the STA transmits the UL MU frame, there is a concernin which quality will be remarkably degraded due to the interference. Inorder to deal with this concern, if signaling information is added to apredetermined field within a preamble of the trigger frame, for example,it is determined in the processing in each of Steps S6 and S7 in FIG. 2that a frame of another BSS is present, and the predetermined signalinginformation is detected from the preamble, control is performed in sucha manner that it is determined that the channel is busy, withoutperforming the CCA threshold, or in such a manner that although thetransmission opportunity is acquired with the CCA threshold control, thetransmission is set to be performed within the duration of the triggerframe. On the other hand, if the signaling information is not detectedin the frame, the setting to the CCA threshold of −66 dBm for the HEformat takes place in the processing in Step S14 in FIG. 2 and theprocessing for channel state determination may be started.

FIG. 6 illustrates a second example of the procedure for the AP 1 toperform the receiving processing in the second embodiment of the presentinvention. It is noted that this holds true for another AP and STA.

In FIG. 6, processing in each of Steps S0 to S9, S14, and S15 are thesame as those in the first example of the procedure for the AP 1 toperform the receiving processing, which is illustrated in FIG. 2.

If in Step S5, the receive frame is not in the HE format (No in S5), theAP 1 checks the BSS ID within a MAC header in the Non-HE format, anddetermines whether or not the BSS ID is consistent with the BSS that theAP1 itself makes up (S21). If the BSS ID is consistent with the BSS thatthe AP 1 itself makes up (S22), the AP 1 continues the demodulation anddefers the simultaneous transmissions. On the other hand, if the BSS IDin the receive frame is not consistent with the BSS that the AP1 itselfmakes up, the setting to the CCA threshold of −76 dBm for the Non-HEformat takes place, the channel state for performing the simultaneoustransmissions is determined (S23), and the demodulation of the receiveframe is stopped (S24).

FIG. 7 illustrates an example of an operation in each of Steps S21, S23,and S24. An example of an operation by the AP 1 that is to be performedwhen the frame in the HE format that is transmitted by the STA 1-2 isreceived after the frame in the Non-HE format that is transmitted by theAP 3 is received is described here.

In FIG. 7, the AP 1 detects the RSSI that is stronger than the receiversensitivity and starts to receive the frame, at time t16, and normallyreceives the preamble of the receive frame, checks that the Non-HEformat is present and checks the MAC header at time t17. Then, at timet18, because it is checked that the BSS ID within the MAC headerindicates another BSS, the setting to the CCA threshold of −76 dBm forthe Non-HE format takes place in the processing in Step S23, and thedemodulation is stopped in the processing in Step S24. In the presentexample of the operation, the AP 1 stops the demodulation when receivingthe frame from the AP 3, but because the RSSI exceeds the CCA thresholdfor the Non-HE format, it is determined that the channel is busy, andthe simultaneous transmissions are deferred.

On the other hand, the STA 1-1 and the STA 1-2 also receive the frame inthe Non-HE format from the AP 3 and stop the demodulation. If thechannel is idle, the STA 1-1 and STA 1-2 possibly perform thetransmission. At this point, if the RSSI from the AP 3 falls below theCCA threshold of −76 dBm for the Non-HE format in the STA 1-2, it isdetermined that the channel is idle, and the frame that is destined forthe AP 1 is transmitted. The AP 1 stops the demodulation of the framefrom the AP 3, at time t18, and detects the RSSI that is stronger thanthe receiver sensitivity and starts to receive the frame, at time t19.

In this manner, the AP 1 stops the demodulation after detecting the BSSID in the frame in the Non-HE format that is transmitted by the AP 3that makes up another BSS, and causes the setting to the CCA thresholdfor the Non-HE format to take place, but because the RSSI of the framethat is transmitted by the AP 3 is stronger than the CCA threshold, thesimultaneous transmissions are deferred without being performed. On theother hand, the STA 1-2 also stops the demodulation after receiving theframe of another BSS, and possibly transmits the frame. Therefore,although the AP 3 is performing the transmission, the AP 1 can normallydemodulate the frame that is transmitted from the STA 1-2.

It is noted that, if the frame in the Non-HE format that is transmittedby the STA 1-3 that makes up the BSS that the AP 1 itself makes up isreceived, because the BSS ID in the received frame is consistent withthe BSS that the AP 1 itself makes up, the demodulation can be continuedin the processing in each of Steps S21 and S22.

Third Embodiment

A feature of the third embodiment is that each type of the receive framein the AP 1 is controlled. At this point, a frame type is read whenreceiving the frame, and is received and demodulated as is. However, thedemodulation is stopped, and thus, it is selected whether or not thesimultaneous transmissions are set to be possible. For example, if adata frame is received, the simultaneous transmissions are positivelyperformed. Although a frame of another BSS is present, if a managementframe is present such as a beacon frame of the AP or an associationrequest frame of the STA, the simultaneous transmissions are kept frombeing performed, and the reception and the demodulation arepreferentially performed. It is noted that because a control frame, suchas an RTS, a CTS, or an ACK, has a short frame time length, theadvantage of switching the control to the simultaneous transmissions isso small that the control frame may be received and demodulated as isand may be utilized for information collection.

FIG. 8 illustrates an example of the procedure for the AP 1 to performthe receiving processing in the third embodiment of the presentinvention. It is noted that this holds true for another AP and STA.

In FIG. 8, processing in each of Steps S0 to S15 are the same as thosein the first example of the procedure for the AP 1 to perform thereceiving processing in the second example, which is illustrated in FIG.2.

In Step S5, if the receive frame is not in the HE format (No in S5), theAP 1 checks the frame type, determines whether or not a frame type or aframe subtype, for example, the management frame, which is necessary forcommunication control by each wireless station, is present (S31),continues the demodulation if the management frame is present (S32), anddefers the simultaneous transmissions. On the other hand, if the dataframe is present, as in the second embodiment that is illustrated inFIG. 2, the setting to the CCA threshold (−76 dBm) for the Non-HE formattakes place, and the channel state is determined (S10). At this point,if the channel is busy (Yes in S11), the demodulation of the data frameis continued (S12) and the simultaneous transmissions are deferred. Onthe other hand, if the channel is idle (No in S11), the demodulation ofthe data frame is stopped (S13), and the state where the simultaneoustransmissions are possible is set to be entered. That is, the thirdembodiment results from adding the processing that preferentiallycontinues the demodulation when the frame in the Non-HE format ispresent and the management frame, such as the beacon frame, is present,to the second embodiment.

FIG. 9 illustrates an operational example of Steps S10 to S13, S31 andS32. An example of an operation by the AP 1 that is to be performed whenthe data frame in the Non-HE format and the beacon frame that aretransmitted by the AP 4 are received is described here.

In FIG. 9, the AP 1 detects the RSSI that is stronger than the receiversensitivity and starts to receive the frame, at time t20, normallyreceives the preamble of the receive frame and checks that the Non-HEformat is present, at time 21, and checks that the frame type within theMAC header is data, at time t22. Because of the checking at times t21and t22, the AP 1 causes the CCA threshold of −76 dBm for the Non-HEformat to take place in the processing in Step S10. In the presentexample of the operation, the AP 1 stops the demodulation when receivingthe data frame from the AP 4, but because the RSSI falls below the CCAthreshold for the Non-HE format, it is determined that the channel isidle, and the simultaneous transmissions are possible.

If the channel is idle until time t23 at which a fixed time+a randomtime have elapsed, the AP 1 transmits the frame that is destined for theSTA 1-1. The STA 1-1 also stops the demodulation, detects the RSSI thatis stronger than the receiver sensitivity, and starts to receive theframe.

The AP 1 detects the RSSI that is stronger than the receiver sensitivityand starts to receive the frame, at time t24, and normally receives thepreamble of the receive frame, checks that the Non-HE format is presentand checks the frame type at time t25. Because it is checked at time t26that the frame type within the MAC header is the management frame, thedemodulation is continued in the processing in Step S32 and the framedemodulation is completed at time t27. If the frame is the beacon frame,the RSSI can be recorded, or BSS information of a transmission sourceAP, or the like can be acquired from information within the frame andthe acquired information or the like can be recorded.

In this manner, in the AP 1, when the simultaneous transmissions areperformed on the beacon frame or an association frame, and thus receiverquality is degraded, because this exerts an influence on a connection tothe wireless LAN itself, the management frame is preferentially receivedand the simultaneous transmissions are kept from being performed.Furthermore, because the beacon frame or the like does not normally useMIMO, the beacon frame or the like is suitable for measurement of theRSSI of the frame that is transmitted from the AP 4. Moreover, the BSSinformation (capabilities or the like) of the AP 4 can be acquired frominformation within the beacon frame.

Fourth Embodiment

A feature of the fourth embodiment is that transmission of each of thestandard of the destination station and transmission of each of thesupported functionalities of the destination station are controlled inthe AP 1. At this point, because a condition for determining whether ornot the frame reception is successful varies according to the standardand supported functionalities of the destination station, as in theembodiments described above, it is selected whether or not to performthe simultaneous transmissions based on information on the standard andsupported functionalities of the destination station to which thetransmission will be made, as well as a state of the receive frame. Forexample, if the destination station is the HE station, although theframe that causes interference is received from another BSS, as in theSTA 1-1 that is illustrated in FIG. 4, the BSSID is identified and thusthe demodulation can be early stopped. For this reason, in thedestination station, although an asynchronous interference frame isreceived preferentially over a desired frame, the demodulation of theinterference frame is stopped and the desired frame is possibly receivednormally. On the other hand, even if the Non-HE station that does nothave this functionality is the destination station, when the CCAthreshold is controlled to be high and is positively transmittedsimultaneously, the desired frame arrives while the demodulation of theinterference frame is in progress. As a result, the reception fails.

FIG. 10 illustrates an example of the procedure for the AP 1 to performtransmitting processing in the fourth embodiment of the presentinvention. It is noted that it is assumed that, in the AP and the STA,the procedure to perform the receiving processing, which is illustratedin FIGS. 2, 6, and 8, is executed. In FIG. 10, the AP 1 starts toprepare for the transmission (S40) and checks a destination of a framethat is scheduled for transmission (S41). At this point, the standardand supported functionalities of the frame that are supportable by thedestination station are checked (S42), and it is determined whether ornot the demodulation of the interference frame is possibly stopped(S43). For example, if the destination station is the HE station, whenthe frame in the HE format is recognized, the BSSID is furtherrecognized in the preamble, and thus it is recognized that a frame fromanother BSS is present, it can be determined that the demodulation ofwhat follows a preamble of the interference frame is possibly stopped.If the demodulation of the interference frame is possibly stopped in thedestination station, CCA threshold control is performed (S44) and thechannel state is determined (S46). For example, as is the case with theCCA threshold control in Steps S10, S14, and S23 in the procedure toperform the receiving processing in each of the embodiments describedabove, control is performed in such a manner that a value which ishigher than the default CCA threshold is obtained, an opportunity forthe channel to be idle is increased, and thus, the simultaneoustransmissions are performed.

On the other hand, if the destination station is the Non-HE station,because the demodulation of the interference frame is impossible tostop, the AP 1 does not perform the CCA threshold control (S45), anddetermines the channel state (S46). For example, without performing theCCA threshold control in Steps S10, S14, and S23 in the procedure toperform the receiving processing in each of the embodiments describedabove, the default CCA threshold may be employed as is, or control maybe performed to employ the CCA threshold at which the interference frameis detectable.

FIG. 11 illustrates an example of operations in Steps S44 and S45. Anexample is described here in which control is performed if the STA 1-1that is the HE station is assumed to be a destination and if the STA 1-3that is the Non-HE station is assumed to be a destination, when it isdetermined in the AP 1 whether or not the simultaneous transmissions areperformed while the frame in the HE format is being received from the AP2.

In (1) of FIG. 11, the AP 1 and the STA 1-1 that are the HE stationsdetect the RSSI that is stronger than the receiver sensitivity, andstart to receive the frame, at time t28. Furthermore, the AP 1 and theSTA 1-1 normally receive the preamble of the receive frame, check thatthe HE format is present, check that the BSSID indicates another BSS,and cause to the setting to the CCA threshold of −66 dBm for the HEformat, at time t29. In the present example of the operation, thereceive frame from the AP 2 is present. Furthermore, because the RSSIfalls below the CCA threshold, it is determined that the channel isidle, the demodulation is stopped, and thus, the simultaneoustransmissions are set to be possible. On the other hand, the STA 1-3that is the Non-HE station detects the RSSI that is stronger than thereceiver sensitivity and starts to receive the frame, at time t28, andnormally receives the preamble of the receive frame, but cannot checkthat the HE format is present, at time t29. Therefore, when the defaultCCA threshold (−82 dBm) is employed as is, because the RSSI exceeds theCCA threshold, the STA 1-3 determines that the channel is busy, and thedemodulation is continued.

If the channel is idle until time t30 at which a fixed time+a randomtime have elapsed, the AP 1 transmits the frame that is destined for theSTA 1-1. The STA 1-1 stops the demodulation at time t29, and detects theRSSI that is stronger than the receiver sensitivity and starts toreceive the frame, at time t30. It is noted that the STA 1-3 which isthe Non-HE station continues the demodulation of the frame from the AP2, but although the demodulation cannot be performed because the frameis in the HE format and the frame in the HE format that is destined forthe STA 1-1 is further received, this does not exert any influence.

Situations at times t28 and t29 in (2) of FIG. 11 are the same as thosein (1) of FIG. 11. The AP 1 and the STA 1-1 receive the preamble of theframe from the AP 2, and then stop the demodulation, but the STA 1-3continues the demodulation of the frame from the AP 2. At this point, ifthe AP 1 transmits the frame in the Non-HE format that is destined forthe STA 1-3 which is the Non-HE station, although the CCA threshold iscontrolled in such a manner that the channel is set to be idle and thetransmission is performed at time t30 as illustrated in (1) of FIG. 11,the modulation cannot be performed in the STA 1-3 that continues thedemodulation of the frame from the AP 2. Therefore, when the AP 1 setsthe CCA threshold to be the default CCA threshold as is withoutcontrolling the CCA threshold, or performs control in such a manner thatthe CCA threshold at which the frame from the AP 2 is detectable isemployed, because the channel is busy in the AP 1, the AP waits toperform the transmission until time t31 at which the AP 2 ends thetransmission and the channel is idle. Accordingly, the normal receptionis possible in the STA 1-3.

Fifth Embodiment

A feature of the fifth embodiment is that transmission of each format ortype of a transmit frame is controlled in the AP 1.

In the fourth embodiment, with the standard and supportedfunctionalities of the destination station for which a frame that istransmitted by the AP1 is destined, it is selected whether or not thesimultaneous transmission are possible, depending on whether or not thedemodulation of the interference frame is possibly stopped. However, ifthe frame that is transmitted by the AP 1 is in the HE format, or is thebeacon frame, the management frame, or the like, the feature of thefifth embodiment, like those of the fourth embodiment, is that the CCAthreshold is controlled and thus that it is selected whether or not thesimultaneous transmissions are set to be possible.

FIG. 12 illustrates a first example of a procedure for the AP 1 toperform the transmitting processing in the fifth embodiment of thepresent invention.

In FIG. 12, the AP 1 starts to prepare for the transmission (S50),checks the format of the frame that is scheduled for the transmission(S51), and determines whether or not the HE format is present (S52). Atthis point, if the frame that is scheduled for the transmission is theHE format, because the frame that is destined for the HE station whichpossibly stops the demodulation of the interference frame is present,the CCA threshold control is performed (S53) and the channel state isdetermined (S55). For example, as is the case with the CCA thresholdcontrol in Steps S10, S14, and S23 in the procedure to perform thereceiving processing in each of the embodiments described above, controlis performed in such a manner that a value which is higher than thedefault CCA threshold is obtained, an opportunity for the channel to beidle is increased, and thus, the simultaneous transmissions areperformed.

On the other hand, if the frame that is scheduled for the transmissionis in the Non-HE format, because there is a likelihood that the framescheduled for the transmission will be the Non-He station that cannotstop the demodulation of the interference frame, the AP 1 does notperform the CCA threshold control (S54), and the channel state isdetermined (S55). For example, without performing the CCA thresholdcontrol in Steps S10, S14, and S23 in the procedure to perform thereceiving processing in each of the embodiments described above, thedefault CCA threshold may be employed as is, or control may be performedto employ the CCA threshold at which the interference frame isdetectable.

That is, if the transmit frame is in the HE format, as is the case withthe transmit frame that is destined for the STA 1-1 that is the HEstation which is illustrated in (1) of FIG. 11, the CCA thresholdcontrol is performed, and thus, the simultaneous transmissions are setto be possible. On the other hand, if the transmit frame is in theNon-HE format, as is the case with the transmit frame that is destinedfor the STA 1-3 that is the Non-HE station which is illustrated in (2)of FIG. 11, the transmission by the AP 2 is ended and the channel isidle, and then the transmission is performed.

FIG. 13 illustrates a second example of the procedure for the AP 1 toperform the transmitting processing in the fifth embodiment of thepresent invention.

In FIG. 13, the AP 1 starts to prepare for the transmission (S50),checks the type of the frame that is scheduled for the transmission(S56), and determines whether or not a frame type or a frame subtype,which is necessary for the communication control by each wirelessstation, for example, the management frame is present (S57). If themanagement frame is not present and for example, the data frame ispresent, the CCA threshold control is performed (S53) and the channelstate is determined (S55). For example, as is the case with the CCAthreshold control in Steps S10, S14, and S23 in the procedure to performthe receiving processing in each of the embodiments described above,control is performed in such a manner that a value which is higher thanthe default CCA threshold is obtained, an opportunity for the channel tobe idle is increased, and thus, the simultaneous transmissions areperformed.

On the other hand, if the management frame is present, because even theNon-HE station that cannot stop the demodulation of the interferenceframe needs to perform the reception, the AP 1 does not perform the CCAthreshold control (S54), and determines the channel state (S55). Forexample, without performing the CCA threshold control in Steps S10, S14,and S23 in the procedure to perform the receiving processing in each ofthe embodiments described above, the default CCA threshold may beemployed as is, or control may be performed to employ the CCA thresholdat which the interference frame is detectable.

That is, if the transmit frame is the data frame, as is the case wherethe transmit frame that is destined for the STA 1-1 which is the HEstation that is illustrated in (1) of FIG. 11, the CCA threshold controlis performed and the simultaneous transmissions are set to be possible.On the other hand, if the transmit frame is the management frame, as isthe case with the transmit frame that is destined for the STA 1-3 thatis the Non-HE station which is illustrated in (2) of FIG. 11, thetransmission by the AP 2 is ended and the channel is idle, and then thetransmission is performed.

The many features and advantages of the embodiments are apparent fromthe detailed specification and, thus, it is intended by the appendedclaims to cover all such features and advantage of the embodiments thatfall within the true spirit and scope thereof. Further, since numerousmodifications and changes will readily occur to those skilled in theart, it is not desired to limit the inventive embodiments to exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope thereof.

The invention claimed is:
 1. A wireless communication station whichtransmits and receives a frame using a predetermined channel by accesscontrol based on carrier sense multiple access with collision avoidance(CSMA/CA) using a clear channel assessment threshold (CCA threshold)considering an interference power from an interfering station which usesthe predetermined channel, wherein: a format that includes anidentification of a basic service set (BSS) in which the wirelesscommunication station belongs to, within a preamble of the frame is anHE format; a control part which checks a format of a frame received at apredetermined receiver sensitivity or above (hereinafter referred to asa received frame), continues demodulation of the received frame if thereceived frame is in the HE format and the identification of BSS of thereceived frame is consistent with its own BSS; and the control part isconfigured to perform carrier sense with a predetermined CCA thresholdfor the HE format if the received frame is in the HE format and theidentification of BSS of the received frame is not consistent with itsown BSS; to stop demodulation of the received frame to transmit a frameif the predetermined channel is idle; and to stop demodulation of thereceived frame to receive a frame if the predetermined channel is busy;wherein the control part is configured, if the received frame is theNon-HE format that does not include an identification of BSS within thepreamble but includes an identification of BSS in a MAC header; toperform carrier sense with a different CCA threshold for the Non-HEformat; to continue the demodulation of the received frame if thepredetermined channel is busy; and to stop the demodulation of thereceived frame to transmit a frame if the predetermined channel is idle.